I installed both 1.1 and 1.2 together and thought that posting the following procedure may be of help to people that wants to keep two versions of OpenFOAM and switch easiely between them,

(1) {platform} folder: you can put here any third party bindary that is needed for any version, since source set the right path;
(2) {user}-{version} and OpenFOAM-{version} folders: are distinguised by their version, so once can include all versions he likes;
(3) change $HOME/.bashrc to point to the required version;
(4) source $HOME/.bashrc;